(a) Field of the Invention
The present invention relates to an organic light emitting diode (“OLED”) display and a method of manufacturing the same.
(b) Description of the Related Art
Recently, thin and light-weight types of monitors and television sets have grown in popularity. Cathode ray tubes (“CRTs.”) have been increasingly replaced by liquid crystal displays (“LCDs”).
However, since the LCD is a non-emissive display device, a backlight is needed in the construction of most LCD displays. Reflective LCDs may use ambient light in order to display images, however they are not ideal for all applications. In addition, LCDs have limitations in their response speed and a viewing angle. Recently, as a display capable of overcoming the aforementioned problems, an organic light emitting diode (“OLED”) display has been proposed.
An OLED display includes two electrodes and a light emitting layer interposed therebetween. An electron injected from the one electrode and a hole injected from the other electrode are combined in the organic light emitting layer to form an exciton, and the exciton discharges energy to emit light.
Since the OLED display is a self-emissive display device, a backlight is not needed. Therefore, the OLED display has an advantage in power consumption and can be manufactured as a thinner structure. In addition, the OLED display has a faster response speed, wider viewing angle, and higher contrast ratio than that of a comparable LCD.
An OLED display can be classified into a passive matrix OLED display and an active matrix OLED display according to its driving mode. Among these, an active matrix OLED display, which uses thin film transistors (“TFTs”) as a switching and driving device to drive each individual pixel, has advantages in that high resolution, low power consumption and a wide screen can be achieved.
An OLED display may further be classified into a bottom emission type display, which emits light to an outside through a bottom substrate, or a top emission type display, which emits light to an outside through a common electrode.
The active matrix OLED display primarily includes the TFT, an organic light emitting member, and partition walls for defining the organic light emitting members into individual pixels.
The partition walls protect the TFT, prevent a light emitting material in a pixel from mixing with another light emitting material in an adjacent pixel, and prevent a short circuit between an anode and a cathode.
However, since the partition walls are formed by a photolithography process, the number of masks for the process increases, thereby increasing manufacturing costs.
In addition, in order to improve the brightness of the OLED display, a light-emission amount per each unit pixel has to be increased, as opposed to the LCD where the output of the single backlight unit can be increased.
In order to increase the amount of light emission, a method of increasing efficiency of a light-emitting material and a method of increasing a current applied to the unit pixel electrode have been proposed.
However, there is a limitation to the efficiency obtainable from a light emitting material. In addition, there is also a limit to the amount of current which can be applied to the unit pixel electrode in order to maintain the lifetime and efficiency of the OLED display and TFT.